This invention relates to a process for dehalogenation of chlorinated aromatic dioxins and related compounds in a safe and economic manner. Since toxicity of chlorinated dibenzo-p-dioxin and many other compounds is reported to be related to the number of halogen atoms, dehalogenation to produce polyphenolic compounds reduces their toxicity. Specifically, 2,3,7,8-tetrachlorodibenzo-p-dioxin is claimed to be highly toxic and the detoxification and destruction method described herein is especially suitable for destruction of that compound.
In the production of 2,4,5-trichlorophenol (2,4,5-TCP), varying amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are produced as a contaminant. The production of 2,4,5-TCP is generally by the dechlorination of symetrical tetrachlorobenzene. This is usually accomplished in the presence of methanolic caustic followed by acidulation of the corresponding phenolate according to the following generalized reactions ##STR1## During the first reaction step varying amounts of dichlorodimethyoxybenzene also are produced, but, in addition, under the reaction conditions, two mols of sodium trichlorophenate may react to yield TCDD according to the reaction ##STR2## By careful distillation the 2,4,5-TCP can be recovered from the reaction mass containing dichlorodimethoxybenzenes and TCDD. The TCDD can also be separated from the 2,4,5-TCP by adsorption on an activated adsorbant such as activated carbon. However, TCDD is claimed to be extremely toxic and cannot readily be disposed of.
No other method of chemical destruction or degradation of TCDD is known which will, quantitatively, safely and economically destroy TCDD in the presence of a wide range of associated materials. TCDD is a highly stable compound. Its destruction by incineration is a possibility which is presently being investigated. However, incineration of a highly chlorinated compound is difficult and does present the possibility of contamination of either the scrubber liquor, the exhaust gases, or any solid residues.
Many methods of chemical destruction of TCDD were investigated, including rupture of the ether linkages, rupture of the aromatic ring structure, chemical oxidation, replacement of the halogen atoms, and ultra-violet light degradation. Throughout this work the complexity of the waste streams containing TCDD interfered with or negated many commonly accepted chemical reaction systems. For example, it is well known that TCDD in dilute proton donating solutions in thin clear films is rapidly decomposed by ultra-violet light. However, the dark viscous streams being investigated yielded little or no TCDD decrease with time. Rupturing the ether linkage with HBr and HI was accomplished only very slowly and incompletely with an extrapolated large expense for reagents.
Replacement of the chlorine atoms with the sodium salt of hydroxyl groups has proven to be fast (a few hours as opposed to days for other methods), safe (can be accomplished at atmospheric pressure with no gaseous emissions to be scrubbed or neutralized), economic (uses cheap raw materials which are readily available), and most of all, complete in a wide range of normally occurring contaminants.
In addition to TCDD, other chlorinated aromatic dioxins and many other chlorinated organic compounds are produced as toxic by-products in the production of industrial organic chemicals. It is obvious to those skilled to the art that these materials may also be disposed of utilizing the concept of this invention.